Two-Point Measurement of High-Frequency Density Fluctuations by Reflectometry in GAMMA 10

To study the detailed radial structure of the Alfvén ion-cyclotron (AIC) waves excited in the GAMMA10 central cell, we upgraded the previously used reflectometer system so as to measure radially separated two density fluctuations simultaneously. Successful application of the new reflectometer system reveals existence of non-trivial radial structure of the AIC waves; from the core to about a half plasma radius, the density fluctuations arising from the AIC waves have common phase relationship, while in the external region, they have opposite phase relation with that of the core.